Mold growing in the attic

I just noticed that there is mold growing on the bottom of the roof sheathing in my attic. I'm not sure what is causing the mold to grow there. I had a new roof put on my house after I bought it, which was less than 9 years ago, and I don't see any evidence of any current leakage from the roof. I'm assuming the mold growth issue is a new problem that has gradually developed over the years, since it's likely I would have noticed it if it was there when I bought the house.
By the way, my bathroom has no fan, so, when I take a shower, the steam stays within the house (one story ranch, only 1000 square feet). Could the mold problem be caused by moisture from the shower making its' way up into the attic? If I were to have a fan installed that vents the moisture outside of the house, do you think there's a chance that this solve the problem (or at least prevent it from getting worse)?
The mold is mainly growing on the sheathing that is on the side of the attic in which the roof has less exposure to the sun. My attic has two vents toward the top of the roof, and two vents on the sides of the attic. I'm skeptical that adding more vents would be of any real benefit.
Anyway, I'm worried, that due to the mold, I may be given a hard time when I sell my house. Other than having a fan direct the moisture from the shower outside the house, and to use an air purifier in the living area, which of the following should I do before selling the house:
1) do nothing, since the mold is in the attic, but fully disclose the problem, and put the house on the market "as is" at a reasonable price.
2) Hire a handyman to scrub off the mold with a fungicide and, if successful, don't mention the mold when selling the house.
3) Hire a handyman to scrub off the mold with a fungicide and fully disclose that there was mold in the attic when selling the house.
4) spend thousands of dollars having a "mold specialist" inspect, test, correct the problem, re-test, and then put the house on the market disclosing that the problem was corrected by a mold specialist. (If I'm mistaken, and mold specialists don't actually charge thousands to correct the problem, then let me know)
Any suggestions would be appreciated.
Thanks.
Jeff
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jeff wrote:

Go here: http://www.allergybuyersclub.com/faqs/moldy-attic.shtml
and here: http://www.ronhungarter.com/ventilation_repairs.html
Or, do a GOOGLE for attic mold or similar.
Correct vetilation is key after cleanup. Jim
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<<Correct vetilation is key after cleanup.>>
My house is only 1000 square feet. Currently there are two square passive vents near the top of the roof and there are two gable vents on the walls on the sides of the attic. One article suggests that having both types of vents is bad. I'm just wondering if anyone disagrees with the idea that both types are always bad.
Anyway, it's strange how the problem is mainly just on the sheathing on side of the attic (the side in which the roof has less exposure to sunlight). That side had a leak in one area around 9 years ago, before I had a new roof put on, so I'm wondering if it's possible that the mold there now is a result what happened back then, or perhaps the mold started growing back then but gradually got worse over the years. Right now it's noticeable but doesn't seem really bad at this point although I fear it will get worse.
Snow can temporarily cover up the vents at the top of the roof, and I wonder if this contributes to the problem. I also wonder if my bathroom's lack of a fan contributes to this problem, since moisture from taking a shower could potentially rise up into the attic.
Anyway, the main question is what type of expert I should call to fully diagnose and solve this problem. (general contractor?) I'd rather hire someone then try to take care of the problem myself. Let me know what type of specialist you recommend I call.
Thanks.
Jeff
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Jeff, I am a home inspector and I ran into this exact situation a few days ago. Your problem sounds like a moisture problem in the attic. Yes, the moisture from your bathroom is finding its way into the attic even though you don't have an exhaust fan; the warm, moist air will find its way into the attic around light fixtures, cracks, etc. When the moist air comes into contact with the cold roof decking the moisture condenses and leaves the decking wet (just what mold needs to grow). The decking on the north side will naturally be colder than on the south side so you will find more mold there. Roof vents and gable vents are not the best combination because they will kind of short circuit the ventilation of the attic. As warm air exhausts through the roof vents cool air will be drawn in through the gable vents causing the air in the attic to not be ventilated properly. (Air should be exhausting through the gable vents, not be drawn into the attic through them.) Your best bet may be to block off the gable vents (screw a piece of plywood over the inside of the vents) and install soffit vents; then you will get proper flow of air through the attic from bottom to top and the air in the attic will be vented much better. You should consider adding an exhaust fan in your bathroom and vent it properly. You can vent it directly to the exterior or you can pipe it to a point close to one of your roof vents (don't place it so it blocks off free flow of attic air through the vent). You may also want to do the same in the kitchen. Also, make sure your clothes dryer vents to the exterior for obvious reasons. Lastly, if you are using a humidifier either stop using it or make sure it is set no higher than 35% or 40% RH (relative humidity); you might even want to consider using a dehumidifier. You may want to hire a home inspector to look things over but I suspect he will tell you the same thing I have told you for free.
Bruce
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